Combustion instabilities frequently are encountered during the development and use of modern industrial gas turbine engines, especially engines that have low NOx technology. These low pollution engines operate at fuel mixtures that can result in combustor instabilities at frequencies up to 700 Hz or even higher. The pressure oscillation caused by the instability can damage the combustor. Often, during engine development, the combustor geometry is modified to correct these instabilities. These modifications are called passive techniques and are generally effective for a limited range of operating conditions. Recently, active control methods have been successfully tested in a laboratory environment. Active control means that some engine parameter, such as engine geometry or fuel flow, is varied at the combustion oscillation frequency but out-of-phase with the instability to dampen the oscillations. A key advantage of the active control system may be the ability to dampen oscillations over a much wider range of engine operating conditions and fuels.
Some active control systems tested to date have used high-speed actuators and valves to pulse fuel flow. For example, magnetostrictive or piezoelectric actuators or high-speed electrohydraulic servo-valves have been used. These valves have proven the theory of active control. However, the technology has not been suitable for commercial production applications. This proposed technology to date is expensive, has performance limitations due to very low stroke, and has limited life.
The state of the art as described above is more fully discussed in the following technical papers and patent application which are hereby incorporated by reference in their entireties: Liquid Injector Actuator for Control of Combustion Processes, AIAA 98-3540, Y. Neumeier, E. Lubarsky, R. Heising, O. Israeli, M. Neumaier and B. T. Zinn, Georgia Institute of Technology, 34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, July 13–15, 1998; Suppression of Combustion Instabilities in a Liquid Fuel Combustor Using a Fast Adaptive Control Algorithm, AIAA 2000-0476, C. E. Johnson, Y. Neumeier, E. Lubarsky, J. Y. Lee, M. Neumaier and B. T. Zinn, Georgia Institute of Technology, AIAA 38th Aerospace Sciences Meeting & Exhibit, 10–13 Jan. 2000; Active Instability Control With Direct-Drive Servo Valves In Liquid-Fueled Combustion Systems, C. Hantschk, J. Hermann and D. Vortmeyer, 26th Symposium (International) on Combustion/The Combustion Institute, 1996/pp. 2835–2841; Active Combustion Instability Control With Spinning Valve Actuator, GT-2002–30042, P. Barooah, T. Anderson and J. Cohen, ASME Turbo Expo 2002, Jun. 3–6, 2002, © 2002 by ASME; Hydraulic R-DDV™ Servovalves, www.textronmotioncontrol.com, Jul. 27, 2001; U.S. Patent Publication No. US 2003/0056490 A1, Anderson et al., VALVE ASSEMBLY FOR USE IN A GAS FUEL NOZZLE, application Ser. No. 09/965,217, Filed Sep. 27, 2001. None of these references have provided a suitable solution for commercial production due to one or more of the following issues: cost, performance limitations, reliability, lifespan concerns, and/or other such concerns. Accordingly, there is a desire for technology that may be employed not just in the laboratory but in commercial applications.